Possible air lock issue on old 4 cyl Mitsu engine

[Greenbeast]

So the next chapter in the Nissan digger, she's started playing up a bit and air locking between running sessions. What could cause this?


She's a bit of a pain to bleed single handedly, i usually have to use some connecting wires to run the fuel pump and manually run the starter while i'm spannering in the back

 

[pycoed]

Leak in one of the feed or return pipes. Leak off pipes the likeliest suspect. Put a bit of clear pipe in the return line & see if you can see air bubbles. Have a good look at the feed line & return line all the way from the tank to the filter & back. If you have an inline prefilter, check that for cracks too.
You could fit a rubber bulb primer in the line (like old Peugots had) to help bleeding.